DE2125677C - Process for the production of highly concentrated nitric acid - Google Patents

Description

For the production of nitric acid according to the Ostwald process, ammonia is catalytically burned with oxygen or excess air to form nitrogen oxide NO, the nitrogen oxide being combined with oxygen still present to form nitrogen dioxide NO ₃ during cooling. Nitrogen dioxide is in equilibrium with dinitrogen tetroxide N ₂ O ₄ . This equilibrium mixture is converted into a 40 to 66% nitric acid solution by adding water and air. When aqueous saipitic acid solutions are distilled, the relative nitric acid content of the vapor increases with increasing temperature, until finally at about 122 ^: C vapor and solution have the same concentration of about 69 percent nitric acid (specific gravity 1.410). This acid is called concentrated nitric acid. By vacuum distillation with concentrated sulfuric acid or magnesium nitrate as. water-binding mine '; this acid can be converted into highly concentrated or anhydrous nitric acid see H ο 11 lma η - Wi berg, textbook of inorganic chemistry. 47th to 56th edition, 1960, pp. 235 to 240, and Ullman-s Encvklopadie der technischen Chemie, Vol. 15 [196 · ', · pp. 31 to 38).

Furthermore, a process for the production of 98: ..- weight percent nitric acid in one piece -.:, Process from oxygen, dilute nitric acid ;! u- ■ and liquid dinitrogen tetroxide under increased ¹ .- ¹ :, pressure known.

The known processes for the production of hoch. ^ - concentrated nitric acid have the following ·; ..: that they additionally z. B. concentrated sulfuric acid; ;: and require oxygen and energy consumption
due to steam and electrical energy considerably: i ::

The object of the invention was therefore to provide a v. .--scientific method for Hersteilung hochkon.:e trated tetroxide 80- to 90 ⁰ / cent nitric acid from Distickstof, dilute nitric acid and air to he '.- wrap, in which the expenditure on apparatus and energ: .- consumption are low and the . ^ nitrogenietroxι. is implemented as fully as possible. This object is achieved by the invention.

The invention therefore relates to a method. for the production of highly concentrated nitric acid

(a) by converting dilute nitric acid nv: dinitrogen tetroxide and air at pressures of 3 to 10 atmospheres and temperatures of 20 to 70 C in N ₂ O ₄ -containing 80 to 90 weight percent nitric acid (acid. A),

(b) Absorbing N ₂ O ₄ -containing gases in 80 to 90 weight percent nitric acid (acid B).

(c) feeding the acid (A) and the acid (B) under pressure into a stripping zone into which air is introduced in countercurrent and nitrous tetroxide is stripped, and

(d) Absorbing the dinitrogen tetroxide not converted and separated in step (a) in an exhaust gas scrubber in the dilute nitric acid used in step (a),

which is characterized in that part of the product obtained in step (c) is returned to step (b) for absorption of the N _a O ₄ -containing gases, the remainder of the product is withdrawn as highly concentrated, 80 to 90 percent by weight nitric acid and that _{the stripped N t} O ₄ -containing air obtained from step (c) _{and the N a} O ₄ -containing dilute nitric acid obtained in step (d) are fed back into step (a).

The method according to the invention essentially consists of the following stages:

2! 25

absä ^! -

ίΐπ>.
you;

Ν, Ο, with air au, N O.-h.i ^ er

K ₂ U ₄ is stripped off.
Stripping the

in

Stripping tower 6 ° u _{3 bis}

Lu: t and

^> _r . _! ';; r _ü hrt _I thatR. ₁ an80-bis90 _£ evMch.,. Pro7em _I ge ic Dc T- ^ n rie te nitric acid, d-.c in the Salreicr- fed air

_{the completed in one}

F ^

N ₁ O ₁ becomes together m, t dr iu! I into the

an agitator 13 and; one

tblsUcher in verJilr.n.er Sa.poter.aure ^ ™ «ng ^ u

_on

a waste gas scrubber 17, not al _{Sa! nelers} acid and air ais »-; -."r; _5nroze nti "e

.... gases are released by ^ c Le.tun «J) .u- ^ ¹ , ..., ^ o ^ denerte, SO- to 90% by weight,

; _mlt nitrogenox.dcn, we NO ur.a NO ,. durcn ^ t UOk ^ _{n man} be. Pressure _-, n of

■ Jiiungl in an N / O.-Absorpt.on.iurm. ^ n- 3, Sa ^ t ^ _{aturcn VO} n 20 bis / ü C a _

.-, In this absorption tower w.rd d ^ Stu. ^ - 3 to ^ _jschen manufacture * ' ^rd .. ^v ° ^rzu ^.

SO, with dinitrogen tetroxide containing oa. Jj ^ _70gewlc hts _P rozentige nitric cn

_n oxygen, which in the ^ s den. ADGA "- e ^^ ^ ^6ü _be5le ^fe _{ht iedoch} no critical: border, for Π-derived gas is contained to N ₁ U ₁ g" tzr t ^ _eingese men diluted SJ

nitric acid g

Panels in

2 and en

P ₂

generated with air.

The resulting N ₂ O ₄ -containing highly concentrated 80- ⁶ "to QOgewichtsprozentige nitric acid (acid B) is then passed through a conduit in the head of a p-NiOj Abstreifturines 6 cingespeis". At the same time, highly concentrated nitric acid (acid A) is fed through line 9 into the dispensing tower 6. This stripping tower 6 contains perforated plates and a heating coil ">. In the stripping tower 6, the air that is fed into its base is the same as the line 8

s | SS

Line 14 passed into the nitric acid synthesis reactor 12. The absorption of the unreacted N ₂ O ₁ in the exhaust gas scrubber 17 (step d) is carried out at pressures of 3 to lOatü and temperatures of from O to 4O ⁰ C. In this way 80 to 90% of the air entrained nitrous oxide becomes. passing through the nitric acid synthesis reactor 12 is absorbed by the dilute nitric acid.

The unabsorbed gases in the exhaust gas scrubber 17 still contain small amounts of N ₂ O ₄ . Therefore, these gases are fed through line 20 into the N ₈ O ₄ absorption tower 2 in order to separate off the remaining N ₂ O ₄ .

As described above, according to the present invention, the absorption and the stripping of the N ₈ O _{4 are} carried out under the same pressure. Therefore, the energy consumption for recycling the absorbent is low. Furthermore, a relatively low waste heat can be used as a heat source for stripping off the N, O _{4 , since the N 1} O _{4 is stripped off} in the presence of the air fed in. In this way, the stripping temperature can be reduced.

The synthesis of the nitric acid is also carried out at essentially the same pressure as the stripping of the nitrous oxide. For this reason, the stripped N ₈ O ₄ can be fed into the nitric acid synthesis reactor 12 as such together with the air fed in. This eliminates the need for complicated devices and operations, such as supplying isolated dinitrogen tetroxide to the reaction system by a pump or a compressor, as is the case with the known methods.

The scrubbing of the exhaust gases in the exhaust gas scrubber 17 (stage d) is also carried out at practically the same pressure as the absorption of the N ₂ O ₄ and the synthesis of the nitric acid. Therefore, the absorption of the unreacted N ₂ O ₄ in the dilute nitric acid fed in and the dilute nitric acid containing _{N 8} O _{4 can also be fed in}

ίο be carried out in the nitric acid synthesis reactor 12 without additional devices, such as a pump or a compressor. There is also no need to regenerate or replenish the absorbent, and both the apparatus and the operations are very simple since some of the nitric acid generated in the nitric acid synthesis reactor 12 can be used as an absorbent for N ₈ O ₄ .
The inventive method thus has the

»O great advantage that the facilities and operations be simplified, the energy consumption is lower and the waste heat through rational utilization, The selection and combination of the starting materials and devices can be effectively exploited.

'5 The example explains the invention.

example

85% by weight highly concentrated nitric acid is produced under the conditions given in the table produced according to the flow sheet of the figure.

table

Device Flow kg / hour A. pressure
atU NO Conc
NO, ntratio
N ₁ O ₁ ι and 2
O, Together
N, η settlement
H ₁ O ENT, unit
the
Percentages tungstcü,
Reference
character no. swiftly
speed
kg-mole / hour EO
le
° c 6.0 5.5 6.1 * 3.4 85.0 Mole percent 1 11.59 25th 6.5 21.0 79.0 Mole percent 8th 3.10 60 6.0 4.3 * 11.2 84.5 Mole percent 20th 2.90 25th 5.7 0.2 * 2.5 97.3 Mole percent 21 10.72 405 15th 0.3 15.0 84.7 Weight per cent 4th 472 10 14.5 12.8 72.7 Weight percent 5 270 20th 25.1 11.3 52.6 Weight percent 9 203 50 0.3 15.0 84.7 Weight percent 10 132 25th 32.0 68.0 Weight percent 18th 25th

Indicated as NO ₁ , however, is a mixture of NO, + N ₁ O ₁ .

1 sheet of drawings

Claims (7)

Patent claims: 1. Process for the production of highly concentrated nitric acid (a) by converting dilute nitric acid with dinitrogen tetroxide and air at pressures of 3 to 10 atmospheres and temperatures of 20 to 70 in N ₂ O _r containing 80 to 90 weight percent nitric acid (acid A), (b) Absorbing N ₂ O ₄ -containing gases in 80 to 90 percent by weight nitric acid (acid B), (c) Feeding the acid (A) and the acid (B) under pressure into a stripping zone into which air is introduced in countercurrent and nitrous oxide? ^{u is} brushed, and _{(d) Absorbing the dinitrogen tetroxide aö} not converted and separated in step (a) in an exhaust gas scrubber in the dilute nitric acid used in step (a), characterized in that part of the product obtained in step (c) is returned to step (b) for absorption of the N, -O ₄ -containing ^ 5 gases, the remainder of the product is withdrawn as highly concentrated, 80-90% by weight nitric acid and in that the stripped N, O _{4 -containing air obtained from step (c) and the N 2} O, -containing dilute nitric acid raised in step (d) are fed back into step (a). 2. The method according to claim 1, characterized in that in step (d) not absorbed Gases used in stage (b) and the nitrogen oxide NO contained in these gases with the Oxygen contained in the unabsorbed gases is oxidized to nitrous oxide. 3. The method according to claim 1, characterized in that the N ₂ O ₁ -containing gases required in step (b) have been generated by catalytic combustion of ammonia with air. 4. The method according to claim 1, characterized in that for the dilute nitric acid required in step (a) a 60- to 70gewichis- 4; percent nitric acid used. 5. The method according to claim 1, characterized in that step (b) by pressing 3 up to 10 atmospheres and temperatures from -20 to -f-50 ° C performs. 6. The method according to claim 1, characterized in that step (c), that is, the stripping of the dinitrogen tetroxide, at pressures of 3 to 10 atmospheres and temperatures of 30 to 100 ⁰ C is carried out. 7. The method according to claim 1, characterized in that step (d) at pressures of 3 to 10 atmospheres and temperatures of 0 to 40 ⁰ C is carried out. 60